Ecological speciation in Darwin’s finches: Ghosts of finches future

The theory of ecological speciation posits that adaptive divergence among incipient species raises incidental barriers to reproduction, thus catalyzing the emergence of new species. Here we conduct an experimental test of this theory in Galápagos finches, a clade in which beaks and mating songs are mechanistically linked. We forecast the acoustic structure of songs for a set of possible evolutionary futures (successive droughts spurring increasingly large beaks) and, in a field assay, presented resulting song simulations to territorial males. We find that responses to song dropped off after 6 simulated drought events, to degrees roughly comparable to drops in response to song divergence caused by cultural drift and acoustic adaptation. Our results support, in Darwin’s finches, the feasibility and mechanistic bases of an ecological speciation hypothesis.

Methods
Behavioral responses of male Geospiza fortis to song playbacks across 4 treatments, and comparing birds' responses to control and probe treatements across 3 studies.